Electret transducers commonly comprise a permanently charged thin plastic film diaphragm that has one surface metallized and is tensioned in close proximity with a conductive backplate with the metallized surface remote to the backplate. The backplate is generally electrically connected to an amplifier circuit, and the metallized surface of the diaphragm is generally electrically connected to ground. While it is highly advantageous to establish these electrical connections as a consequence of the physical assembly of the components of the electret transducer, we are unaware of any electret transducer design other than that disclosed in Fraim et al U.S. Pat. No. 3,816,671 where this is accomplished.
Fraim et al U.S. Pat. No. 3,816,671 discloses an electret microphone including an apertured backplate having a peripheral ridge and a conductive surface within the ridge that extends through the apertures to the underside of the backplate. An electret diaphragm having an outwardly facing metallized surface is bonded to the peripheral ridge while under tension, and a conductive ring is positioned on the periphery of the diaphragm in engagement with the metallized surface. In addition, a closure plate having a preamplifier circuit thereon is positioned beneath the backplate, and a compressible conductive member that is bonded to the closure plate and electrically connected to the input of the preamplifier circuit, is positioned between the closure plate and the conductive surface on the underside of the backplate. A conductive housing disposed about these elements engages the conductive ring. The conductive housing is swaged against a conductive surface of the closure plate to connect the conductive ring to the ground lead of the preamplifier and to press the compressible conductive member against the conductive under-surface of the backplate.